Modified PLA Homochiral Crystallites Facilitated by the Confinement of PLA Stereocomplexes

The crystallization and melting behaviors of polylactide (PLA) homochiral polymer under the confinement of stereocomplex crystallites were studied in the linear and three-armed poly(d-lactide)/poly(l-lactide) (PDLA/PLLA and 3PDLA/3PLLA) solution casting blends. WAXD results showed that novel modified crystallites formed when PLA homopolymer crystallized from the melting state. And the modified crystallites formed in 3PDLA/3PLLA blends (M-A) were less stable than that formed in similar PDLA/PLLA blends (M-B) after specimens cooled at a specific rate. Although these modified crystallites differed from PLA α crystallites (M-C), both of them transformed into α crystallites during heating. The transitions among different crystallites revealed the multiple melting behaviors in DSC measurement. The type of PLA homochiral crystallites and their contents mainly depended on the D/L compositions, annealing conditions, molecular weights, and architectures of the polymers in the blends. The formation of these modified crystallites should be ascribed to the confinement of PLA stereocomplex and steric hindrance of polymers, and PLA homopolymer could not charge into lattice orderly during rapid crystallization.